Primary schools have presided over a "shocking" increase in obesity among children as young as four, health campaigners warned yesterday.
Nearly one in four children (22.9 per cent) are obese or overweight by the time they start school aged four or five. But this rises to almost a third by the time they are 10- to 11-year-olds (31.6 per cent), according to figures released by the Government.
The proportion of obese children nearly doubles during primary school, from 9.9 per cent aged five to 17.5 per cent aged 11.
Campaigners argued that pupils were not getting enough exercise because of the pressure to focus on targets and tests. They said parents and teachers had forgotten what a "normal weight" looked like because so many children were overweight.
Tam Fry, of the Child Growth Foundation, said it was a "national scandal" that the proportion of overweight children was allowed to grow by nearly 10 percentage points during their primary school years.
"A lot of this is simply down to the fact that children aren't getting enough exercise. We need to make physical activity a core subject. Somebody has got to decide what we want. Do we want brilliant mathematicians who can read and write well but are so fat that they die early? Or do we want well-rounded children who are fit enough to be parents and hold down jobs?"
Dr David Haslam, clinical director of the National Obesity Forum, said it was "extremely alarming" that obesity rates nearly doubled during children's formative years while they were in primary schools.
He argued that if you went into a school playground you would not pick out many children as overweight. "Our perception of weight has changed. We're looking at overweight children and not seeing them as overweight."
The figures, recorded in 2006-07, showed that in both reception year (age four to five) and year six (age 10 to 11), boys were more likely than girls to be obese.
London had the highest rate for both groups – 11.3 per cent in reception and 20.8 per cent in year six. The south-east coast had the lowest rate for reception (8.5 per cent), and the South-west the best for year six, 14.9 per cent.
A Department of Health spokesman said the Government's recently published £372m obesity strategy would help everyone lead healthier lives.
Dawn Primarolo, the public health minister, said: "We're not going to stem the tide overnight but through measures such as providing the right information and support to parents to ensure a healthy diet and regular exercise for children and increasing participation in sport and healthy eating, we hope to support families to lead healthier lives."
Kevin Brennan, the children's minister, said 86 per cent of children now enjoyed at least two hours of PE and sport each week.
"We now have plans to increase this to five hours each week by 2011," he added.
However, the problem of childhood obesity could be even worse. Even though 80 per cent of children were weighed as part of the Government's child measurement programme, the research shows that most of the 20 per cent who were not were the heaviest children, whose parents opted out of the exercise.
Childhood obesity: the facts
Nearly one in four children (22.9 per cent) was found to be either obese or overweight.
Almost a third of children (31.6 per cent) were found to be either obese or overweight.
* In both age groups more boys than girls were found to be overweight.
* London has the highest rate of obesity among the young, followed by the south-east coast of England and the South-west region.
* 48 per cent of children were weighed for 2005-06 figures and 80 per cent – 876,416 – for 2006-07 figures.